In an existing waterproof electronic control device, a waterproofing structure of, in particular, a connector periphery is such that a groove or depressed portion is provided in a case that comes into contact with an outer periphery of the connector, an O-ring, which is a waterproofing member, is fitted in the groove or depressed portion, and a sealing agent is applied, whereby airtightness is secured by the connector outer periphery and a case being caused to adhere closely across the waterproofing member (refer to Patent Document 1).